The nuclear magnetic resonance experiment

The small difference in population among the Af/ or Ms levels allows the magnetic resonance experiments. From now on we will focus on the nuclear magnetic resonance experiment, but little would be changed if we dealt with EPR. 

The nuclear magnetic resonance phenomenon was first observed through a continuous wave experiment [2-6]. Resonance between the two Mj levels of an / = V2 nucleus (without loss of generality) in a magnetic field Bo can be achieved by applying a magnetic field rotating with a frequency (see Eqs. (1.12) and (1.16)) such that 

The time average component in the xy plane is zero. The frequency a is the frequency of precession about z and is the resonance frequency (o = 2nv). Indeed, if we send r.f. with exactly that frequency, the vector senses the external magnetic field as well as the r.f. field. The magnetization vector undeigoes a 

---

D. I. Hoult, R. E. Richards 1976, (The signal-to-noise ratio of the nuclear magnetic resonance experiment), J. Magn. Reson. 24, 71. 

Aqueous GPC can also be semiprepped in manner just like nonaqueous GPC. In this case one must consider carefully the buffers, salts, and biocides used in the eluant. If the fractions are destined for nuclear magnetic resonance experiments it will be imperative to either reduce the salt concentration in the eluant or remove salt after the initial fractionation. Likewise, if the collected samples are destined for infrared (IR) analysis, it is important to choose salts and buffers that have good IR transparency in the wavenumber ranges of interest. 

The models in Figures 2 and 3 show that a part of the low molecular weight liquid obviously separates the polymer chains from each other, thus facilitating segment mobility. Another part of it fills the cavities and displays almost liquid state behavior in them. This rather simplified model of the glass structure has been verified in some by nuclear magnetic resonance experiments. 

D. The table below shows signal-to-noise ratios recorded in a nuclear magnetic resonance experiment. Construct graphs of... 

The previous three chapters have shown that nuclear magnetic resonance experiments with 1H and 13C nuclei are enormously useful to the chemist working with organic compounds. There is no need, however, to limit ourselves to these two important nuclei. Indeed, there are 120 different nuclei whose spin number, /, is greater than zero and, therefore, theoretically observable in an NMR experiment. Of these 120 nuclei, 31 of them are dipolar, which means that their spin number is one-half (/ = ). 

The application of Fourier transform methods to nuclear magnetic resonance experiments improved the signal-to-noise ratio and permitted extraction of data heretofore inaccessible. 

Recent single-molecule experimental studies of proteins provide more detailed views of protein motions, and confirm that a wide variety of timescales is involved in, e.g., catalytic action of enzymes [7,14,15,19,33], Of course, molecular dynamics simulations have been used to probe motions in single proteins for many years, and advances in both theory and computational science have made simulations a powerful approach to building theoretical understanding of protein dynamics [1], The recent introduction of accelerated molecular dynamics methods is helpful in this context [11]. Although detailed dynamical information is sacrificed to the enhanced sampling of conformational space in these methods, which have been shown to access conformational fluctuations that are revealed by nuclear magnetic resonance experiments on the millisecond... 

Saturation transfer difference nuclear magnetic resonance experiments have shown that there is a strong interaction between the enzyme and the (R)-enantiomers of the alcohols, but not the (S)-enantiomers (H. W. Anthonsen, unpublished results). As described above, addition of a small amount of pure (R)-alcohols increased the 5-value of kinetic resolution and, moreover, the effect disappeared quickly. The reason is probably that the alcohol moves into the active site where it is esterified. A future goal is to find an additive that can bind irreversibly to this unknown allosteric site, thus causing a lasting effect. 

---